Molecular hybridization of cellular RNA with unique sequences of DNA is being employed as a measure of gene expression in several model systems in which modification of nervous system - related functions are manipulable by environmental modification or disease states. In mostly preliminary data several model systems have shown promise of providing easily measureable changes in gene expression (RNA diversity). These include: (1) visual cortices and brain stems of kittens whose eyelids are sutured closed; (2) whole brains of rats raised in enriched vs. impoverished environments; (3) morphological and physiological differences under different growth conditions in cultured cell lines of neural or muscle origin; and (4) muscle and nerve tissue from normal mice and those with hereditary muscular dystrophy. The studies are continuing.